1. Field of Endeavor
The present invention relates to batteries and more particularly to a low temperature sodium-beta battery.
2. State of Technology
Prior art high-temperature sodium-beta (Na-(3) batteries have achieved energy densities comparable to the best Li-ion batteries, with specific power comparable to that of the majority of commercially available cells. A reversible liquid-phase anode, coupled with a solid-state Na-ion conductive electrolyte, has enabled the Na-sulfur battery to achieve a cycle life of 2,250 cycles at 100% depth-of-discharge and 4,500 cycles at 80% depth-of-discharge, and the Na-metal chloride battery to achieve even higher cycle life. The high-temperature sodium-beta (Na-(3) batteries have been used in electric vehicles (EVs) and could potentially be used in deep-sea rescue vehicles. The primary challenge for these batteries is the need for high-temperature operation necessary to-keep-the anode-above the melting-point of sodium. Approximately 10% of the batteries' energy is used to keep the battery heated to the relatively high core temperature, and the specific energy and energy density are further compromised by the need for thermal insulation.
Referring now to the drawings and in particular to FIG. 1, an example of a prior art high-temperature sodium-beta (Na-(3) battery is illustrated. The battery is a high temperature liquid anode and cathode battery designated generally by the reference numeral 100. The battery includes the following components: current collector 10 which can be made of stainless steel 304 or 316, electrical insulation 12, outer casing 14, heat insulation 16, inner casing, cathode 20, separator/electrolyte 22, and anode 24. The battery 100 is usually made in a tall cylindrical configuration. The battery 100 is enclosed by a steel casing 14 that is protected from corrosion on the inside.
U.S. Pat. No. 4,975,344 issued to Roger J. Wedlake and Johan Coetzer Dec. 4, 1990 provides the state of technology information reproduce below:
This invention relates to electrochemical power storage cells. More particularly, the invention relates to an electrochemical power storage cell which is rechargeable and which has a molten alkali metal anode [negative electrode] separated by a separator from a cathode which comprises an electronically conductive electrolyte-permeable porous matrix which is impregnated with a liquid electrolyte and which has electrochemically active cathode [positive electrode] material dispersed therein.
The Applicant is aware of cells of the type described above, in which the separator is tubular in shape, having the cathode inside the tube and the anode outside the tube, or vice versa. When the cathode is outside the separator it is generally also tubular in shape, and when it is inside the separator it may be tubular or cylindrical. Typically, in such cells, the maximum capacity is determined by the size of the sealed hollow interior of the separator tube, which defines the maximum size of the electrode [cathode or anode as the case may be] located in its interior. For efficiency as regards volumetric energy density, which is related to the parameter [Ah/m.sup.3], and indeed mass energy density, which is related to the parameter [Ah/kg], the interior space of the separator must be completely filled by the electrode occupying it, so that such cells are typically designed to have the separator tube completely filled by one of the electrodes, the other electrode, outside the separator tube, being designed to have a matching capacity. The cell thus has, for a particular cathode material and anode material, a single value for its capacity, and hence a single value for the parameter capacity/unit area separator surface, at which there is maximum volumetric energy density and maximum mass energy density.
Such cells, designed to have their separator tubes completely filled by one of the electrodes, thus suffer from substantial inflexibility as regards varying, for a fixed diameter of separator tube, the value of capacity/unit area of separator surface. This value cannot be increased, as the electrode in the separator tube cannot be enlarged, and the value of capacity/unit area of the separator surface can only be reduced inefficiently. While it is straightforward efficiently to reduce the capacity of the electrode outside the separator tube by reducing its radial thickness or volume, a corresponding reduction in capacity of the electrode inside the separator tube causes problems. Either the separator tube will be incompletely filled, leading to a volumetric energy density penalty, or it will contain electrode material which cannot be discharged and is dead weight, leading to both mass energy density and volumetric energy density penalties.
It follows thus that to alter the value of the parameter capacity/unit area of separator surface, while keeping the separator interior completely filled with an electrode which can be fully discharged so as to maintain optimum mass- and volumetric energy density, it is necessary to alter the diameter of the separator tube. However, substantial expense is involved in tooling up to make tubes of the type in question, involving the use e.g. of stainless steel precision-made mandrels and matching membranes for isostatic pressing of tubes on to the mandrels. The expense of altering tube diameter is often prohibitive and severely restricts design flexibility with regard to varying the value of the parameter capacity/unit area of separator surface, while maintaining efficient mass- and volumetric energy density. Such variation is however desirable for various different cell applications.
United States Published Patent Application No. 2010/0279174 by Edgar D. Young published Nov. 4, 2010 provides the state of technology information reproduce below:
Another metal that has been investigated for use in batteries as an alternative to lithium is sodium. Sodium is attractive for such use because of its high reduction potential, its low weight, its non-toxic nature, its relative abundance and ready availability, and its low cost. In order to construct practical batteries, the sodium must be used in liquid, or molten, form and must be kept isolated from moisture, including humidity in ambient air.
An example of a commercially viable sodium battery was developed in 1985 by the Council for Scientific and Industrial Research in Pretoria, South Africa. The battery, which was invented by the Council's Zeolite Battery Research Africa Project (nicknamed “ZEBRA”), is described, among other places, in U.S. Pat. No. 4,975,344, the entire disclosure of which is hereby incorporated by reference. The ZEBRA battery includes an anode of molten sodium, an electrolyte of molten sodium chloroaluminate (NaAlCl4), a cathode of nickel or another transition metal in the discharged state (a metal chloride when charged), and a ceramic separator of sodium ion-conducting beta-alumina to prevent contact between the molten sodium anode and the NaAlCl4 electrolyte. The technical name for the battery is sodium-nickel chloride (Na—NiCl2) battery, but it is commonly referred to as the “ZEBRA battery.”
The ZEBRA battery's liquid electrolyte solidifies below its melting point of 157° C. (314.6° F.), and the normal operating temperature range is typically between 250° C. (482° F.) and 350° C. (662° F.). The β-alumina solid electrolyte (BASE) that is employed as a membrane, or separator, within this system is very stable, both to the sodium metal anode and the sodium chloroaluminate electrolyte. The primary elements used in the manufacture of ZEBRA batteries—that is, sodium, chloride, and aluminum—have much higher worldwide reserves and annual production than the lithium used in lithium-ion batteries discussed above.
One potential shortcoming of the ZEBRA battery, which may prevent its widespread adoption, is the reliance upon nickel as the cathode material. The estimated world reserves of nickel are on the order of about eight hundred million tons, closer to those of lithium (twenty-eight million tons) than magnesium (eight billion tons). Worldwide adoption of the ZEBRA battery as the primary type of automotive battery would quickly deplete the available global reserves, thereby reinforcing the need for a battery that utilizes more abundant materials.
Accordingly, a need exists in the industry for a durable battery made of readily abundant materials, which may be easily assembled and repeatedly recharged.